The invention relates generally to a storage system and a data rearrangement method suitable for use in, for example, a storage system where data is backed up between storage systems.
A method managing plural hard disks utilizing RAID (Redundant Array of Independent/inexpensive Disks) format is conventionally used in storage systems that store data using storage apparatuses. At least one logical volume is formed in a physical storage area provided by a number of hard disks.
Recently, a “dynamic storage area allocation” technique, i.e., a technique of not creating a logical volume with a fixed capacity using a storage area in hard disks, but providing a host computer with a virtual volume using plural logical volumes and dynamically allocating a storage area in the logical volumes to the virtual volume in response to a request from a host computer has been proposed (for example, see Japanese Patent Laid-Open Publication No. 2003-015915).
However, if a new storage area in a logical volume is added to a virtual volume using the “dynamic storage area allocation” technique, the amount of data stored may vary depending on the logical volumes used for the virtual volume, and, as a result, access will possibly concentrate in some specific logical volumes and the performance when responding to requests from a host computer may deteriorate as a whole.
In that regard, for example, a data rearrangement technique for improving the performance when responding to requests from a host computer by averaging the data amounts stored in logical volumes used by a virtual volume and rearranging data stored in those logical volumes has been proposed. However, when implementing that data rearrangement technique, the data rearrangement is executed after temporarily stopping the host computer from sending requests. Accordingly, requests from the host computer cannot be received during the data rearrangement process, and the response performance deteriorates.